//         https://ac.nowcoder.com/acm/contest/5600/H




#include <iostream>
using namespace std;

int main()
{
    char x;
    int a[123] = { 0 };
    while (cin >> x)
    {
        if (x >= 'a' && x <= 'z')
            a[x]++;
    }
    int ans = 0;
    for (char i = 'a'; i <= 'z'; i++)
    {
        if (a[i] > ans)
        {
            ans = a[i];
            x = i;
        }
    }
    cout << x << endl;
    return 0;
}